In the 3GPP (3rd Generation Partnership Project) which is the standardization organization for mobile communications systems, the specifications of a new communications method which is provided as a communications method different from W-CDMA, and which is referred to as long term evolution (LTE, E-UTRAN), as to a wireless section, and is also referred to as “system architecture evolution” (“System Architecture Evolution” SAE), as to a whole system structure including a core network have been developed. In the case of LTE, an access method, a radio channel configuration and protocols different from those of the current W-CDMA (HSDPA/HSUPA) are provided. For example, as the access method, the W-CDMA uses code division multiple access (Code Division Multiple Access), whereas the LTE uses OFDM (Orthogonal Frequency Division Multiplexing) for a downlink direction and uses SC-FDMA (Single Career Frequency Division Multiple Access) for an uplink direction. Furthermore, W-CDMA has a bandwidth of 5 MHz, whereas the LTE can adopt bandwidths of 1.25/2.5/5/10/15/20 MHz. In addition, LTE adopts only a packet switching method, instead of circuit switching as used in the W-CDMA.
In the case of LTE, because a communications system is configured using a new core network different from a core network (referred to as General Packet Radio System GPRS) for use in the case of W-CDMA, the LTE is defined as a radio access network independent from a W-CDMA network. Therefore, in order to distinguish from a W-CDMA communications system, in an LTE communications system, a base station (Base station) which communicates with a mobile terminal (UE User Equipment) is called eNB (E-UTRAN NodeB, which is also referred to as eNodeB), a base station control apparatus (Radio Network Controller) which performs an exchange of control data and user data with a plurality of base stations is called aGW (Access Gateway, which is also referred to as Mobility Management Entity: MME or Serving Gateway: S-GW). In this LTE communications system, point-to-multipoint (Point to Multipoint) communications, such as a multicast and broadcast type multimedia service which is referred to as an E-MBMS (Evolved Multimedia Broadcast Multicast Service), are carried out, and a communications service, such as a unicast (Unicast) service for each mobile terminal among a plurality of mobile terminals, is also provided. In the case of LTE, because no dedicated channels (Dedicated Channel or Dedicated Physical Channel) destined for each mobile terminal exists in transport channels and physical channels, unlike in the case of W-CDMA, transmission of data to each mobile terminal is carried out via a shared channel (Shared Channel).
When data transmission has occurred in either an uplink or a downlink, scheduling for enabling communications between the base station and the mobile terminal is carried out for either the uplink or the downlink. For example, in the downlink scheduling, the base station allocates radio resources according to the size of data which have occurred or the channel quality to the mobile terminal, and sets up a modulation method and an error correcting code method (MCS: Modulation and Coding scheme) according to target quality and data speed. In the uplink scheduling, when data to be transmitted to the base station have occurred in the mobile terminal, the mobile terminal transmits a signal (uplink scheduling request SR: Scheduling Request) for making a request for allocation of uplink radio resources, and, in response to the request, the base station allocates uplink radio resources to the mobile terminal. Control signals used for such scheduling control for enabling communications between the mobile terminal and the base station via a radio link include an upper layer signal, such as an “L3 control signal (information)” (Layer3 control signaling or an L3 message), and a signal which is referred to as an “L1/L2 control signal (information)” (Layer1/Layer2 control signaling). An L3 control signal is mainly notified from, for example, an upper layer, such as an RRC layer, at the time of initial transmission including the time of occurrence of a call connection (RRC Connect), and is used to, via a downlink, perform a setup of uplink channels or downlink channels, or allocation of radio resources. On the other hand, an L1/L2 control signal is frequently exchanged between the mobile terminal and the base station via both an uplink and a downlink. An uplink scheduling request signal with which the mobile terminal makes a request of the base station for allocation of radio resources via an uplink is an L1/L2 control signal. Also at the time when changing the radio resources irregularly according to change in the data size or requirements on the quality of a channel, including the time of occurrence of a call connection and the time of continuation of a call connection, an L1/L2 control signal is used. As L1/L2 control signals, there are a response signal (Ack/Nack) which, when, for example, receiving data, the base station or the mobile terminal uses in order to notify the reception results to the communications partner, and quality information CQI (Channel Quality Indicator) showing the quality of received data or the quality of a channel. Furthermore, in the case of LTE, a support of MIMO (Multiple Input Multiple Output) has been studied. In a case in which MIMO is supported, L1/L2 control signals also include MIMO related information.
Ack/Nack included in L1/L2 control signals is a signal for HARQ (Hybrid Automatic Repeat Request) which causes the receive side to decode data, which the receive side has failed in demodulating, without discarding the data and by combination with data retransmitted thereto. When an Ack signal is notified from the receive side to the transmit side, new packet data are transmitted from the transmit side to the receive side. In contrast, when a Nack signal is notified from the receive side to the transmit side, packet data are retransmitted from the transmit side to the receive side. Within this specification, a simple expression of Ack/Nack denotes above-mentioned Ack/Nack for HARQ.
In Chapter 4.2 of nonpatent reference 1, mapping of downlink control channel information (Downlink Control Channel Information) onto a PDCCH (Physical Downlink Control Channel) which is a physical channel is described.
Furthermore, in Chapter 4.1 of nonpatent reference 2, a frame structure in a downlink, as shown in FIG. 1 is described. One sub-frame is formed of two slots (refer to FIG. 1). In FIG. 1, each hatched portion shows a PDCCH mapping region. In Chapter 5.5.4 of nonpatent reference 2, mapping of a PDCCH onto the first three OFDM symbols (refer to each hatched portion shown in FIG. 1) of the first slot of each sub-frame is described. In this specification, downlink control channel information which is mapped onto a PDCCH is referred to as L1/L2 control information (signal). In addition, as information included in L1/L2 control information, there are (1) Ack/Nack, (2) L1/L2 control information for uplink communications control (UL-related L1/L2 control information, uplink grant (ULGRANT), etc.), and (3) L1/L2 control information for downlink communications control (DL-related L1/L2 control information, downlink allocation information (DL Allocation)).
Furthermore, nonpatent reference 3 describes that downlink control channels (downlink control channel information) are configured of an aggregation (Aggregation) of control channel elements (Control Channel Elements: CCEs). In addition, nonpatent reference 3 describes that when receiving a downlink control channel, a mobile terminal monitors a candidate set (Candidate Set) of downlink control channels. Nonpatent reference 3 further describes that the number of candidates included in the candidate set determines the maximum number of times that the mobile terminal performs a detecting operation (Blind Detect). As to this candidate set, nonpatent reference 4 discloses a method of enabling a base station and a mobile terminal to determine the candidate set without using explicit signaling from the base station to the mobile terminal. In nonpatent reference 5, a mapping method of mapping CCEs onto a physical resource is described. Concretely, a method of performing cell (base station)-specific scrambling and then performing common interleave is described.
On the other hand, in nonpatent reference 6, a method of interleaving (interleave) a plurality of PDCCHs into resource blocks (RB Resource Blocks) on which different power control operations are performed respectively, and performing mapping of the plurality of PDCCHs distributedly for every determined RBs is disclosed. Nonpatent reference 6 further discloses that each RB is configured of all of the region of the first three OFDM symbols of one sub-frame, and a mobile terminal carries out a decoding process without using information (the value of Cat.0, Cat: Category) showing how many symbols (OFDM symbols) in the head region of the first slot of one sub-frame are used. The purpose of the method is to make it easy to perform power control in order to reduce the amount of interference with adjacent base stations, and is further to make it possible for the mobile terminal to start a receiving process of receiving the PDCCHs regardless of the value of Cat.0. Furthermore, in nonpatent reference 7, a method of inserting an index (index) of Ack/Nack into downlink control channel information (UL GRANT) which is used for allocation of uplink resources is described.
An LTE core network is a network via which a packet connection is established, and user data, including real time data, such as voice data, are all packetized in an LTE core network. In a case of transmission of general packet data, real time performance is not required of the general packet data, and the data speed at which the general packet data are transmitted and received varies irregularly according to the description of the data. In contrast, because real time data, such as voice data, have to be reproduced in real time by the communications partner even if the real time data are packetized, real time data having a predetermined size are produced at fixed time intervals. Therefore, at the time of communications of general packet data and at the time of communications of real time data, such as voice data, different scheduling methods are needed for allocation of radio resources with scheduling.
For data, such as general packet data, which are transmitted at a speed which changes according to the description of the data, and which need to be subjected to high speed communications, a dynamic scheduling (dynamic scheduling) method of being able to dynamically change the settings of radio resources for every sub-frame according to channel quality and data speed (data size) is used. When carrying out dynamic scheduling, a base station notifies information about allocation of uplink and downlink radio resources to a mobile terminal by using an L1/L2 control signal.
In contrast, because communications in which data requiring real-time performance, such as voice data, having a predetermined size are produced at fixed time intervals are carried out at a low speed and the size of the data is determined from one or more predetermined sizes, a persistent scheduling (Persistent scheduling) method of being able to allocate radio resources at regular intervals and continuously is used for such communications.
In the 3GPP, as to the persistent scheduling (also referred to as semi-persistent scheduling (semi-persistent scheduling)), a setup of periodicity and so on from a base station to a mobile terminal by using RRC (Radio Resource Control) has been discussed (nonpatent reference 8). It can be considered that a base station allocates a frequency domain to a mobile terminal by using a PDCCH (an L1/L2 control signal) at intervals (in a cycle) set up by using RRC (referred to as persistent intervals (a persistent cycle) from here on). Furthermore, allocation of radio resources only during a talk (Talk spurt) (also referred to active (active)) even if persistent scheduling is being carried out, and release of radio resources during a silent period (Silent Period) (also referred to as de-active (de-active)) have been discussed. The use of a PDCCH (an L1/L2 control signal) for a base station to notify that there is a transition to active or de-active as mentioned above to a mobile terminal has been discussed (nonpatent reference 9).
Nonpatent reference 1: TS36.212 V1.2.0 (R1-072635)
Nonpatent reference 2: TS36.211 V1.1.0 (R1-072633)
Nonpatent reference 3: 3GPP contributions R1-071223
Nonpatent reference 4: 3GPP contributions R1-072220
Nonpatent reference 5: 3GPP contributions R1-072613
Nonpatent reference 6: 3GPP contributions R1-072088
Nonpatent reference 7: 3GPP contributions R1-072120
Nonpatent reference 8: 3GPP contributions R2-080088
Nonpatent reference 9: 3GPP contributions R2-080163
Nonpatent reference 10: 3GPP TS36.300 V8.2.0